Optimization And Performance Analysis Of Autonomous Integrity Monitoring Algorithm For GNSS Receiver

With the construction and maintenance of Global Navigation Satellite Systems(GNSS),the number of satellites visible to users is also increasing.GNSS has been able to meet the basic positioning needs of most ordinary users.However,in the field of life safety,users not only value the positioning accuracy of navigation satellites,but also pay more attention to the safety and reliability of the entire navigation system.In order to ensure the reliability of the navigation system,it is necessary to monitor its integrity.Therefore,this paper first introduces the principles of Receiver Autonomous Integrity Monitoring(RAIM)and Advanced Receiver Autonomous Integrity Monitoring(ARAIM),and improves and optimizes the deficiencies of some algorithms.Through the measured data and simulation,the effectiveness of the algorithm is evaluated and verified,and the performance of the current GNSS ARAIM is analyzed.The main work carried out and results achieved in this article are as follows:1.In view of the problem of unavailability of sliding window RAIM in some epochs when there is a pseudorange deviation,the strategy of Hatch filtering to reduce the error in the unit weight of the posterior is used to improve the usability of sliding window RAIM.An improved Hatch filter smoothing algorithm is proposed.The experimental results show that the accuracy of the improved Hatch filter smoothing algorithm is better than the traditional Hatch filter and the Hatch filter based on height angle,which has a good pseudorange repair effect and improves the utilization rate of the satellite;and when the pseudorange has a gross error of 20 m and 40 m,the improved Hatch filter algorithm is used to reduce the number of epochs of sliding windowed RAIM from 25 and 91 to 0 and 17,respectively.It shows that when there is a pseudorange gross error,the improved Hatch filtering can improve the usability of sliding windowed RAIM.2.The basic ARAIM algorithm distributes the continuity risk and intact risk probability equally to all visible satellites,resulting in a more conservative Vertical Protection Level(VPL),making single constellation insufficient for Localizer Performance with Vertical guidance down to 200 feet service(LPV-200).The approach requires integrity.Based on this,a maximum minimization method is adopted,which can reasonably allocate intact risk and continuity risk.The results of calculation examples of the measured data show that the maximum minimization method is better than other optimization algorithms in improving the availability of ARAIM under LPV-200.The average improvement rate of standard deviation is about 80%,the average improvement rate of VPL is more than 10%,and the improvement rate of ARAIM availability is more than 5%.Global simulation results show that after using the maximum minimization method,the coverage of GPS ARAIM availability greater than 99.5% has increased from 0% to 17.35%;the coverage of BDS ARAIM availability greater than 99.5% has increased from 19.91% to 22.33%.3.Due to the difference in GNSS constellation performance,the threat model to be considered by ARAIM after GNSS combination is more complicated,and it is of great practical significance to evaluate GNSS ARAIM performance in time.Based on this,this paper analyzes the ARAIM performance of the GNSS double constellation,the three constellation,and the four constellation combination when only double star failures and single star and single constellation failures occur at the same time.The ARAIM performance of the ground station is analyzed through measured data,and further simulate global ARAIM availability.The actual measurement and simulation results show that,compared with the double star failure,when the single star and single constellation failures occur simultaneously,the ARAIM availability of the double constellation decreases greatly;the ARAIM availability of the three constellation and the four constellations decreases less,and the ARAIM availability near the equator higher.As a heterogeneous constellation,the combination of BDS and other constellations takes into account wide faults.Only when GPS is included in other constellations,the availability in the Asia-Pacific region will be significantly higher than in other regions.